Oscillation devices including a piezoelectric vibration element, such as a quartz vibrator, have been widely used. The piezoelectric oscillation device strongly requires that the oscillation frequency vary little. Accordingly, piezoelectric oscillation devices are measured for resonant frequency, oscillation frequency and other properties after being manufactured, and the piezoelectric oscillation devices having those properties outside permissible ranges are rejected as defectives. Also, if the resonant frequency or oscillation frequency of a measured piezoelectric oscillation device is outside a permissible range, it is attempted to adjust the frequency of the piezoelectric oscillation device.
For example, the below-cited PTL 1 teaches that in manufacture of quartz vibrators, the quartz vibrator is mounted on an insulating substrate and then a small amount of silver is vapor-deposited on the surfaces of electrodes so that the frequency can be adjusted. After adjusting the frequency, in addition, the quartz vibrators are subjected to vacuum lock by vacuum heat baking, followed by ageing, and then the quartz vibrators are screened through the measurement of their electrical properties.
Furthermore, PTL 1 teaches that in such a method, attachment of dust or particles in the manufacturing process is likely to degrade one or more of the properties or to increase the variation of the property. Accordingly, PTL 1 discloses a method for adjusting the frequency by cutting the surface of the electrode of the quartz vibrator chip with plasma.
PTL 1: Japanese Unexamined Patent Application Publication No. 10-284968